This application relates generally to the field of rigid magnetic disc drive data storage devices, and more particularly, but not by way of limitation, to a head suspension for mounting and supporting a head assembly in a disc drive, and for providing dynamic control of the flying attitude of the head assembly.
Disc drives of the type known as “Winchester” disc drives or rigid disc drives are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path.
As the physical size of disc drives has decreased historically, the physical size of many of the disc drive components has also decreased to accommodate this size reduction. Similarly, the density of the data recorded on the magnetic media has been greatly increased. In order to accomplish this increase in data density, significant improvements in both the recording heads and recording media have been made.
For instance, the first rigid disc drives used in personal computers had a data capacity of only 10 megabytes, and were in the format commonly referred to in the industry as the “full height, 5¼″ format. Disc drives of the current generation typically have a data capacity of over a gigabyte (and frequently several gigabytes) in a 3½″ package which is only one fourth the size of the full height, 5¼″ format or less. Even smaller standard physical disc drive package formats, such as 2½″ and 1.8″, have been established. In order for these smaller envelope standards to gain market acceptance, even greater recording densities must be achieved.
The recording heads used in disc drives have evolved from monolithic inductive heads to composite inductive heads (without and with metal-in-gap technology) to thin-film heads fabricated using semi-conductor deposition techniques to the current generation of thin-film heads incorporating inductive write and magneto-resistive (MR) read elements. This technology path was necessitated by the need to continuously reduce the size of the gap in the head used to record and recover data, since such a gap size reduction—and an associated reduction in write current—was needed to reduce the size of the individual bit domain and allow greater recording density.
Since the reduction in gap size and write current also meant that the head had to be closer to the recording medium, the quest for increased data density also lead to a parallel evolution in the technology of the recording medium. The earliest Winchester disc drives included discs coated with “particulate” recording layers. That is, small particles of ferrous oxide were suspended in a non-magnetic adhesive and applied to the disc substrate. With such discs, the size of the magnetic domain required to record a flux transition was clearly limited by the average size of the oxide particles and how closely these oxide particles were spaced within the adhesive matrix. The smoothness and flatness of the disc surface was also similarly limited. However, since the size of contemporary head gaps allowed data recording and retrieval with a head flying height of twelve microinches (0.000012 inches, 12μ″) or greater, the surface characteristics of the discs were adequate for the times.
Disc drives of the current generation incorporate heads that fly at nominal heights of only about 1.0μ″, and products currently under development will reduce this flying height to 0.5μ″ or less. Obviously, with nominal flying heights in this range, the surface characteristics of the disc medium must be much more closely controlled than was the case only a short time ago.
It is common in the industry to move the head assemblies to designated park location when the disc drive experiences a loss of power. In a first class of disc drive, this park location is associated with ramp structures adjacent the outer diameters of the discs, and the head assembles are “parked” on the ramp structures, out of contact with the discs. Such disc drives are capable of withstanding large amounts of applied mechanical shock, and are frequently used, therefore, with laptop computer systems.
A second class of discs drives, often referred to as “contact start/stop” or CSS drives, park the head assemblies at a designated “landing zone” near the inner diameters of the discs, where user data is not stored.
As the surfaces of the discs has become progressively smoother—in order to increase areal recording density, as noted above—it has become problematic to park the heads on the disc surface due to increased static friction, or “stiction”, between the extremely smooth air bearing surfaces of the head assemblies and the extremely smooth disc surfaces.
It has, therefore, become a common practice in the industry to provide a textured surface in the landing zones of the discs. Early examples of texturing in landing zones were created using mechanical abrading techniques, but as dictated by the flying heights necessary for current recording densities, most current generation landing zone texturing is produced using lasers, which apply a multitude of “bumps” with controlled size and spacing in the landing zones.
Once again, as the data recording zones of the discs became smoother and smoother, it was necessary to reduce the “roughness” of the landing zones, in order to enable the head assemblies to fly into the landing zones, and reducing the roughness of the landing zone has lead back to the problems of stiction which the textured surfaces of the landing zones were intended to alleviate.
It would be desirable, therefore, to be able to fly the head assemblies at low levels over the data recording areas of the disc, and dynamically alter the flying height to a greater level when it becomes necessary to park the heads, in order to allow the landing zones to continue to have a greater degree of texturing.
It should also be noted that a second approach to minimize stiction involves fabrication of sliders for head assemblies that include textured contact surfaces. Such head assemblies do not require the addition of texturing in the designated landing zone, since the texturing is carried along with the head assembly itself. The present invention, however, is also useful with such head assemblies to compensate for radial position dependent variations in head flying height, as will be discussed in more detail hereinbelow.
It has also become a common practice in the industry to provide a plurality of data recording zones radially arranged across the disc, to increase the total data storage capacity of the disc drive. Such “zone bit recording” or “constant linear density recording” schemes allow data at the outer zones of the discs to be recorded at the same linear density as at the inner zones, in spite of differences in the linear velocity between the head assemblies and the discs in these areas.
However, the difference in linear velocity as the head assemblies are moved outward tends to cause the head assemblies to fly higher, reducing the effectiveness of the heads in recording and retrieving data.
Similarly, skew effects associated with the common rotary actuators described above also contribute to variation in head flying heights with radial position of the head assemblies over the discs.
It would also be desirable, therefore, to be able to dynamically control the flying attitude of the head assemblies—and thus the flying height—to allow the heads to fly higher at a relatively “rough” landing zone, and to compensate for flying height variations caused by differences in relative linear velocity and skew angles between the head assemblies and the discs.
The present invention is directed to providing a head suspension which includes features for dynamically controlling the flying attitude of the head assemblies, and thus controlling the flying height of the head assemblies.